Properties of Cytoelirome bo 511 



flavin on the resonance system of the haem group. The bands at 567 and 

 533 mn are unhkely to be due to a semi-quinone form of the flavin group. 

 Such semi-quinone intermediates, observed in some flavoproteins, have a 

 rather weak band at about 560 m// but show no band near 533 m// (see 

 Beinert, 1957) whereas a well defmed two-banded spectrum is observed with 

 the transient form of cytochrome ho. Tliis also suggests that the haem, as 

 well as the flavin group, is functional in the lactate dehydrogenase activity of 

 cytochrome b^. Kinetic studies, as discussed below, provide evidence con- 

 sistent with this interpretation. 



The Deoxyribose Polynucleotide Conipoiient of Crystalline Cytochrome b.^ and 



the Nucleotide-Protein Link 



The crystalline cytochrome b^, of Appleby and Morton (1954, 1959a) has 



a prominent absorption band at 265 m/* (see Table 4 and Figs. 2 and 3). 



This is due to a deoxyribose polynucleotide, which is not dialysable, and 



which is about 6 % of the dry weight of the material (Appleby, 1957 ; Morton, 



1955a, 1958; Appleby and Morton, 1960). It contains about 15 nucleotide 



residues/mole of haem. Re-crystallized cytochrome b^ contains no ribose or 



adenine + thymine . 



uracil (Table 1). The molecular ratio of : : — m the poly- 



guanme + cytosme 



nucleotide is 2-60 and in yeast deoxyribonucleic acid is 1-79 (Appleby and 



Morton, 1960; Montague and Morton, 1960). The polynucleotide is a 



unique and integral component occurring in constant amount in different 



batches of crystalhne cytochrome b.^.* 



More recently, Nygaard (1958) has found dialysable and non-dialysable 

 ribonucleotides associated with non-crystalline cytochrome b^. This type 

 of material remains in the mother liquor when cytochrome b^ is crystallized 

 (Appleby and Morton, 1960). 



The deoxyribose polynucleotide is not essential for lactate dehydrogenase 

 activity of cytochrome b^. It may be split from the enzyme by digestion with 

 deoxyribonuclease ; by precipitation of the protein with ammonium sulphate ; 

 and by electrophoresis at a suitable pH (Appleby and Morton, 1960). The 

 function of this component is not known. Uptake of ^sp-labelled inorganic 

 phosphate during lactate oxidation is not catalysed by cytochrome /?2 (Appleby 

 and Morton, 1960). 



ENZYMIC PROPERTIES OF CRYSTALLINE CYTOCHROME b^ 



Substrate Specificity 



Armstrong and Morton (1959) have shown that crystalline cytochrome b<2_ 

 catalyses reduction of ferricyanide by a number of a-hydroxy-monocarboxylic 



* Added in proof. The polynucleotide has been obtained as homogeneous material of 

 molecular weight approx. 10,000 (Montague and Morton, 1960). 



